Fuel injection system and control valve for multi-cylinder engines

ABSTRACT

A fuel injection system and control valve are disclosed for use with a multi-cylinder engine such as a diesel or proco type engine. The disclosed control valve, which is of the piezoelectric type, controls the fuel injection into the individual cylinders by being connected in fluid circuit between the high pressure pump and distributor which are contained in the pump and distributor assembly. The control valve contains novel features providing improvements in the system.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention pertains to engine fuel systems and is particularlyconcerned with a novel fuel injection system and control valve.

The disclosure contains a number of novel features which contribute toimprovements in a fuel injection system. One feature of the inventionrelates to ambient compensation for the piezoelectric actuator elementof a control valve which controls fuel injection into the cylinders of amulti-cylinder engine in cooperation with a fuel pump and distributorassembly. The ambient compensation is provided by circulating fuelthrough a sealed enclosure of the valve which contains the piezoelectricelement therein. Further detail relates to the specific construction ofthe valve which provides for the ambient compensation capability. Thesefeatures, along with additional features, advantages and benefits of theinvention, will be seen in the ensuing description and claims which areto be considered in conjunction with the accompanying drawings. Thedrawings disclose a preferred embodiment of the invention according tothe best mode presently contemplated in carrying out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a fuel injection systemembodying principles of the present invention.

FIG. 2 is a longitudinal sectional view taken through the control valveused in the system of FIG. 1.

FIG. 3 is a top view of the control valve of FIG. 2.

FIG. 4 is a bottom view of the control valve of FIG. 2.

FIG. 5 is a sectional view taken in the direction of arrows 5--5 in FIG.2.

FIG. 6 is an enlarged fragmentary view of a portion of FIG. 2.

FIGS. 7A, 7B and 7C should be considered together and constitute aschematic diagram of electrical control system for controlling the valveof FIG. 2, in the operative system shown in FIG. 1.

FIG. 8 is a waveform illustrating operation of the valve of FIG. 2 inthe system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 there is disclosed a fuel injection system 10 embodyingprinciples of the present invention. The main elements of system 10comprise a pump and distributor assembly 12, a plurality of nozzles 14,which correspond in number to the number of cylinders of the engine withwhich the system 10 is used, (only one nozzle is shown in the drawingsfor sake of clarity), a control valve 16 and a fuel tank 18. Alsoincluded in the system are a filter assembly 20, a check valve 22, asurge tank 24, a high pressure regulator valve 26, and a low pressureregulator valve 28. A drain line 30 connects to a number of thesecomponents for draining fuel back to tank 18. A supply line 32 which mayinclude a supply pump 34 supplies fuel from tank 18 to certain of thecomponents; particularly, the supply line 32 connects to the inlet offilter 20 and to one inlet of control valve 16 through a flow controlorifice 35. A line 36 connects from the outlet of filter 20 to the inletof the low pressure, or boost, pump section 38 of pump and distributorassembly 12. The boost pump 38 serves to boost the pressure of the fuelreceived from pump 34 and supplies fuel to the high pressure pumpsection 40 of pump and distributor assembly 12. The high pressure pumpsection 40 pressurizes the fuel even further and delivers this highpressurized fuel via a line 42 to the inlet of check valve 22. Theoutlet of check valve 22 in turn connects via a line 44 through a seriessurge tank 24 to another inlet of control valve 16. Surge tank 24 servesto dampen pump pulsations and provide delivery of adequate volumes ofpressurized fuel to the engine when injection occurs. The high pressureregulator valve 26 is also connected to line 44 and serves to regulatethe pressure of the fuel at this point in the system. Another line 46connects the outlet of control valve 16 to the distributor section 48 ofpump and distributor assembly 12. Briefly, when valve 16 is actuated,fuel is delivered from the pump and distributor assembly 12 via thelines 42, 44 through check valve 22 and surge tank 24 to control valve16, and flows through valve 16 and out line 46 back to assembly 12. Eachinjector 14 is connected to an appropriate outlet of the distributorsection 48 by means of a line 50 whereby each injector 14 issequentially hydraulically connected in circuit with the pressurizedsupply of fuel when valve 16 is actuated. Another outlet of controlvalve 16 connects via a line 52 to the low pressure regulator valve 28to reduce a pressure in nozzle line 50 to prevent after-injections, aswill be explained more fully later in the description.

The pump and distributor assembly 12 is a conventional commerciallyavailable unit which has been slightly modified. In the commerciallyavailable unit the connection from the high pressure section to thedistributor section is contained internally of the assembly. However,control valve 16, in the illustrated embodiment is external to assembly12 and therefore the commercially available assembly 12 is modified tothe extent of separating the internal connection between the distributorand the high pressure pump outlet and making these available forexternal connection whereby the outlet of the pump may be fed outthrough the circuit comprised of line 42, check valve 22, line 44,including the surge tank, control valve 16 and line 46 back to inlet ofthe distributor section 48. The assembly 12 is driven by the engine andis so synchronized therewith that the injectors 14 are selectivelyconnected in sequence to valve 16. As will be explained in greaterdetail hereinafter, control valve 16 is electrically controlled by acontrol signal applied to the input terminal leads 54, 56 so that theprecise amount of fuel and the timing thereof in relation to thecylinder operating cycle is electrically controlled. Thus, the inventionprovides an improvement in the control and operation of the fuelinjection system of the engine. With this description of the system,attention can now be directed to details of control valve 16 as shown inFIGS. 2, 3, and 4.

Control valve 16 may be considered as comprising a number of valve bodyelements including a first element 58, a second element 60, a thirdelement 62, a fourth element 64, a fifth element 66 and a sixth element68. The second element 60 is of generally tubular shape and includes anelectro-expansive actuator 70 disposed within the bore 72 thereof. Theelectro-expansive actuator 70 is in the form of a piezoelectric stackcontaining a plurality of individual piezoelectric discs constructed inaccordance with known techniques. The electro-expansive actuator isintended to be electrically energized by the application of anelectrical potential across the leads 54, 56 supplied from an externalsource. When so energized, the electro-expansive actuator expandsaxially a predetermined amount thereby providing the actuation for thecontrol valve. The use of a piezoelectric stack is particularlyadvantageous in that a large actuating force can be developed with ashort response time. A piston 74 is disposed for axial displacement byactuator 70, the actuator having its upper end lodged within a recess 76in the first element 58 and its other end lodged within a recess 78 inthe upper face of piston 74. Piston 74 is disposed for a close slidingfit within the bore section 80 of element 60. A suitable O-ring seal 82is lodged in a corresponding groove extending circumferentially aroundthe outside of piston 74 to provide for sealing of the piston withinrespect to the bore 80. A radially inwardly directed circumferentialflange 84 is provided at the lower end of element 60 and is disposedradially inwardly of bore 80. A set of Belleville springs 86 is disposedas shown in the drawing between flange 84 and piston 74 tending to biasthe latter upwardly toward actuator 70, as viewed in FIG. 2. It will beobserved that the overall diameter of actuator 70 is somewhat less thanthe inside diameter of bore 72 so that an annular space 88 is providedaround the outside of the actuator. An inlet port 90 is provided in theside wall of element 60 and a pair of outlet ports 92 in element 58 sothat cooling fluid may be circulated within the space 88 to absorb heatfrom the actuator 70 during operation of the valve. Element 58 forms atop or cover for the valve and is assembled to element 60 by means of aplurality of bolts 94 which are passed through suitable holes in element58 to engage registering tapped holes in the flange disposed around theoutside of the upper end of element 60. An O-ring seal 96 is disposed ina corresponding groove around the outside of bore 72 in the top face ofelement 60 to be compressed between elements 58 and 60 as the bolts 94are tightened to thereby seal around the upper end of space 88 betweenthe two elements 58 and 60.

The lower end of element 60 includes a reduced diameter section whoseoutside diameter is provided with a thread 98. A threaded counterbore100 is provided at the upper end of element 62 with the two elements 60and 62 being threaded together by means of the threads 98 and 100. Thisthreaded attachment provides for relative axial adjustment between thetwo elements 60 and 62 and provides an advantageous way to adjust theoperating elements of the valve as will be explained in greater detailhereinafter. Once the desired axial adjustment has been attained, thetwo elements 60 and 62 are locked together to prevent relative rotation.The locking arrangement is provided at the matching opposed flanges 102and 104 of the two elements 60 and 62 respectively. Flange 102 extendscircumferentially around the outside of the wall of element 60 andincludes four threaded holes 106 and four adjacent locating holes 107(see FIG. 5) extending completely through flange 102 and parallel to theaxis of the valve, each locating hole 107 being associated with acorresponding hole 106. Both types of holes 106, 107 are centered on acommon circuit which itself is concentric with the valve axis. Theangular relationship between the threaded holes 106 and locating holes107 is shown in FIG. 5. Each of four set secrews 108 is threaded into acorresponding hole 106 and may be adjusted by means of an appropriatetool (such as by a a hexagonal wrench) engaging the upper end of the setscrew as viewed in FIG. 2. A plurality of equally circumferentiallyspaced holes 110 are provided in flange 104 as shown in FIG. 4. Theholes 110, which are of like diameter, are centered at 15° intervals ona common circle which is concentric with the valve axis and of the samediameter as the circle on which holes 106, 107 are centered. With thelower end of the set screws 108 disposed vertically above the uppersurface of flange 104, the two elements 60 and 62 may be freelyrelatively rotated with respect to each other to perform the axialadjustment. If, once the desired adjustment has been attained, one ofthe locating holes 107 is in alignment with one of the holes 110, thethreaded hole 106 associated with that one locating hole 107 is also inalignment with one of the holes 110 so that the set screw 108 in theassociated threaded hole 106 may be advanced to insert the lower endthereof into the corresponding aligned hole 110 thereby locking the twoelements 60 and 62 together. If one of the locating holes 107 is inalignment with a hole 110, the two elements 60 and 62 may be relativelyrotated to bring the next nearest hole 110 into alignment with one ofthe four holes 107. The set screw 108 in the corresponding hole 106 isthen advanced to insert the lower end thereof into the correspondinghole 110 thereby locking the two elements 60 and 62 together. Byproviding a plurality of holes 110 at uniform 15° increments aroundflange 104 and the offset threaded holes 106 and adjacent holes 107around flange 102 in the pattern illustrated, the two elements 60 and 62are angularly positionable for locking the increments of 3° 45' ofrotation. For a given pitch of thread of 40 threads per inch this meansthat adjustments in the range of 0.25 thousands of an inch can beattained.

Element 62 is also of generally tubular shape comprising a throughborecontaining a number of bore sections. Disposed within the bore section112 is the valve element 114. Valve element 114 is constructed from afirst piece 116 and a second piece 118. The two elements 116, 118 areassembled together by providing a theaded stud section 120 on piece 118which is threaded into a bore section 122 provided in the shank of piece116. The two pieces are threaded together until the shoulders abut eachother as indicated at 124. The upper end of piece 116 is provided with ahexagonal head and the lower end of piece 118 is provided with ahexagonal socket in the lower face thereof, both of which permit the useof fastening tools to tighten the two pieces 116, 118. If desired, alocking arrangement such as a nylon insert may also be provided toassist in locking the two pieces together after they have been fullytightened. Preparatory to assembly of the two pieces, a set ofBelleville springs 126 is disposed over the shank of piece 116 so thatwhen assembled the springs 126 engaged the head of the valve element tobias same upwardly as viewed in FIG. 2. A high pressure seal, such as aT-seal, 128 is provided as shown to seal around the valve element 114. Avalve seat 130 is provided at the lower end of bore section 112 and thehead 132 of the valve 114 (provided by the second valve piece 118) iscaused to seat on seat 130 because of the upward bias imparted to valveelement 114 by springs 126. As shown in FIG. 2, valve element 114 ispositioned with head 132 seated on seat 130; however, with the valveproperly adjusted the lower face of piston 74 is disposed as close aspossible to the head of valve element 114, with the electro-expansiveactuator 70 not energized, without causing the valve head 132 to unseatfrom seat 130. Because of the fine adjustment feature described above,it will be appreciated that essentially the full displacement of piston74, when actuated by energization of electro-expansive actuator 70, willbe imparted to valve 114.

Valve 114 serves to control flow between an inlet 134 and an outlet 136which are both provided in the side walls of element 62. The inlet 134intersects the bore section 112 at a location which is above seat 130 asviewed in FIG. 2 and outlet port 136 intercepts the enlarged boresection at a point below seat 130. Thus, when valve 114 is open (i.e.,unseated from seat 130) flow is permitted from inlet 134 to outlet 136,and when valve 114 is closed (i.e., seated on seat 130), the flow isblocked. As can be seen in greater detail in FIG. 6, the diameter acrossseat 130 (dimension B) is less than the diameter across bore 112(dimension A). Thus, when actuator 70 is de-energized, fluid pressureacting on valve 114 will exert an upward force tending to close thevalve. This is an advantageous feature since it promotes positiveshut-off of flow to the injectors upon de-energization of the actuator.

Body element 64 is secured to the lower face of element 62 by means of aplurality of bolts 138 which pass through appropriate holes in element64 to engage corresponding trapped holes in element 62. Preferably, asealing gasket 140 is provided between the two elements 62 and 64 asshown. Element 64 is provided with a threaded throughbore 142 which isin alignment with the bore of element 62. Element 66 includes apartially threaded shank 144 which is threaded into the bore 142 ofelement 64. An O-ring seal 146 is lodged in a suitable groove extendingaround the outside of the unthreaded distal end of shank 144 to providea seal between the two elements 62 and 66 as indicated. Disposed withinthe bore section 148 of element 66 is a generally tubular seat element150. The upper end of seat element 150 is provided with a seat 152against which the lower end of the head 132 of valve 114 may seat.Element 66 is provided with a threaded bore section 154 into which athreaded section 156 of element 68 is threaded. The distal end of theshank of element 68 protrudes upwardly through the bore of element 66and a set of Belleville springs 158 is disposed between the upper end ofelement 68 and the lower end of seat element 150. Element 68 is adjustedto cause seat element 150 to be biased upwardly within the bore section148 toward the head 132 of valve 114 with the flange which extendsaround the outside of element 150 at the lower end thereof abutting theshoulder within the bore of element 66. The amount of compression of thespring set 158 may be varied by the thickness of gasket 155 betweenelement 68 and element 66 to thereby vary the downward force required todisplace seat element 150 downwardly relative to element 66. A highpressure seal 160 is disposed in a suitable groove in element 66 toprovide for sealing between the outside wall of seat element 150 and theinner wall of element 66. A drain port 162 is provided at the side ofthe lower end of element 66. Element 68 includes an axial passage 164intersected by a radial passage 165 to provide communication of thedrain 162 with the path defined by the inner diameters of seat element150 and the Belleville springs 158 for a purpose hereinafter explained.A locking nut 166 is threaded onto the thread 144 of element 66preparatory to threading of the latter into the threaded bore 154. Oncethe desired adjustment of element 66 on element 64 has been attained,the locking nut 166 may be tightened against element 164 to lock the twoelements 64, 66 in place. The adjustment of element 66 on element 64 ismade in such a manner that spring-loaded seat 152 is disposed slightlybelow head 132 with the valve de-energized, (i.e., head 132 is notseated on seat 152). The distance between head 132 and seat 152 is smallenough however that head 132 will seat at seat 152 when the valve isoperated by energization of actuator 70. Any overtravel will be taken upby the downward displacement of seat element 150 against springs 158.The pre-tension imparted to springs 158 by the adjustment of element 68ensures seating closure between head 132 and seat 152 on the downwarddisplacement of element 150. In other words, the fuel pressure acting onseat element 150 is insufficient to open the path to drain when thevalve is energized.

FIGS. 7A, 7B, and 7C illustrate an electrical control circuit foroperating control valve 16. FIGS. 7A and 7B illustrate an electroniccontrol unit. Turning first to FIG. 7A, a speed signal representative ofthe engine speed is developed by means of a transducer 200 disposed inproximity to the toothed flywheel 202 which rotates with the enginecrankshaft. The disclosed transducer 200 is energized from a suitable DCpower supply via two lead wires and a third lead wire supplies a pulsetype signal waveform 204 as flywheel 202 rotates. The signal is composedof individual pulses with each pulse corresponding to one tooth. It willbe appreciated that the frequency of the pulses of waveform 204 istherefore representative of the rotational speed of flywheel 202, andhence representative of engine speed. The waveform 204 is passed througha buffer circuit 206 to attenuate noise components which may be in thewaveform. The buffered signal is then supplied to trigger a monostable,or one-shot, circuit 208. The one-shot circuit 208 is designed toproduce a fixed time duration output pulse in response to the leadingedge of each pulse of waveform 204. The fixed width of the monostableoutput pulse is, of course, less than the maximum anticipated frequencyof the waveform 204. By thus providing a fixed duration output pulse, arectangular pulse train waveform is developed at the output of one-shot208 wherein the average value of the waveform is representative ofengine speed. The waveform from one-shot 208 is passed through anotherbuffer circuit 210 to remove noise and the buffered signal is suppliedas an input to a velocity amplifier circuit 212. The velocity amplifiercircuit serves to develop a DC output voltage whose magnitude isproportional to the average value of the buffered signal received fromthe buffer 210, and hence representative of the speed of the engine. Thesignal level from the velocity amplifier 212 is supplied to anintegrator circuit 214. The integrator circuit 214 serves to integratethe velocity signal and thereby tend to develop a ramp type voltage.However, the integrator is reset at predetermined intervals whereby thesignal appearing at the output of the integrator assumes a sawtoothshape as shown in the drawing.

The circuit for resetting the integrator circuit comprises a series ofstages which are driven from a magnetic pick-up 216 and rotary cam 218.The rotary cam 218 comprises a number of lobes equal to the number ofcylinders in the engine with which the circuit is used, and issynchronized with engine rotation to cause the transition of each lobeof the cam 218 past the pick-up device 216 in timed relationship withthe operation of the pistons in their respective cylinders. The pick-updevice 216 is energized from a DC supply and develops a signal waveform220 which is utilized to reset the integrator. As each lobe sweeps pastthe pick-up device 216, there is a sharp transition in the signal andthis occurs in the middle of each of the bi-polar pulses constitutingthe waveform 220. It is this specific transition which causes theintegrator to be reset. Signal 220 is supplied to a pulse amplifier andlimiter circuit 222 and thence to a buffer circuit 224. Each transitionin the waveform 220 creates a similar transition at the output of buffer224. The signal from buffer 224 trips a second one-shot 226. Desirably,the widths of the pulses of this one-shot are narrow in relation to theangular range represented by the frequency of the pulses at maximumengine speed to promote maximum accuracy in resetting the integrator.The one-shot pulses are supplied through a buffer 228 and a pulseamplifier 230 to reset the integrator circuit 214.

The sawtooth signal from integrator 214 is supplied to both a pilotstage circuit 232 and a main stage circuit 234. (See FIG. 7B.) The pilotstage circuit 232 includes a comparator circuit 236 and a one-shotcircuit 238. Likewise the main stage circuit includes a comparatorcircuit 240 and a one-shot circuit 242. A pilot crank angle control 244is associated with comparator 236 and a main pulse crank angle control246 is associated with comparator 240. Normally, the adjustment of thepilot crank angle control provides a less positive voltage reference tothe non-inverting input of comparator 236 than does the main crank anglecontrol to the corresponding input of comparator 240.

If it is assumed that the sawtooth is beginning a ramp cycle, a pointwill be reached where there is a coincidence between the pilot crankangle control signal and the sawtooth. This causes the comparator output236 to swing, and in turn causes one-shot 238 to deliver an outputpulse. The width of the output pulse of one-shot 238 is controlled by apulse width control 248. As will be seen, the pulse width output ofone-shot 238 causes valve 16 to open and supply a corresponding pilotpulse of fuel to the appropriate cylinder of the engine. As the sawtoothcontinues to ramp a point is next reached where coincidence is achievedbetween the main crank angle control signal and the sawtooth. Thiscauses the output of comparator 240 to swing and hence causes one-shot242 to produce an output pulse. The output pulse of one-shot 242 has awidth determined by a pulse width control adjustment 250. The pulsewidth control adjustment 250 is normally set to produce a wider pulsethan does the pulse width control 248 of the pilot pulse circuit.Accordingly, the output pulse of one-shot 242 causes valve 16 to openfor a considerably longer duration than did the pulse from one-shot 238whereby the pilot pulse of injected fuel is followed by a subsequentmain injection of a considerably larger amount of fuel. (See FIG. 8).

A selector switch 252 is provided whereby the injector may beselectively controlled in accordance either with the pilot pulse, themain pulse or both pulses. For the particular selection setting ofswitch 252, the selected signal (or signals) is (or are) suppliedfurther to a summing and inverting amplifier 254 and from there to aninverting amplifier 256. With this arrangement the occurrence of eithera main pulse or a pilot pulse or both at the input of amplifier 254 willproduce a corresponding main or pilot pulse or both at the output ofinverting amplifier 256. Each output pulse from amplifier 256 issupplied to a power amplifier stage 260. The power amplifier stage is inturn coupled to a high voltage pulse supply unit for actuating theelectro-expansive element 70 of valve 16.

The high voltage pulse supply unit is shown in FIG. 7C. This circuitincludes input leads 262, 264 which are coupled to power amplifier stage260 to receive the output pulse from the electronic control unit. Inorder to actuate the piezoelectric element forming the electro-expansiveactuator 70 it is necessary that a source of fairly high potential beavailable. Such a source is designated by the reference numeral 266 inFIG. 7C. By way of example, this source may be constructed in accordancewith known techniques to develop a high voltage from a device which maybe driven by the engine, such as an alternator with appropriateregulating and rectifying circuitry for developing a high potentialsuitable for actuating the piezoelectric stack. Because thepiezoelectric stack is energized only on an intermittent basis, therebyhaving a relatively short duty cycle, it is desirable to utilize acapacitor 268 across the power supply which may be charged to thedesired potential during the portion of the cycle preceding the firingof the stack. The charge developed across the capacitor is utilized toenergize the piezoelectric stack which may require an operating voltagesuch as approximately 1000 volts DC. The unique arrangement of the highvoltage pulse supply shown in FIG. 7C is such that the 1000 voltpotential required for the stack can be developed with a lesser voltageacross capacitor 268, for example in the range of 400 to 450 volts DC.Connected between capacitor 268 and the stack is a circuit including anSCR 270 and a pair of inductors 272, 274. The gate-cathode circuit ofSCR 270 is coupled via a coupling transformer 276 to receive the signalfrom the electronic control unit supplied via leads 262, 264. It will beappreciated that the windings of the transfer 276 are so connected inrelation to the lines 262, 264 that the positive pulse supplied by theoutput of power amplifier 260 causes SCR 270 to be switched intoconduction. With SCR 270 in conduction, the charge on capacitor 268 isdrawn as current through the SCR and the inductors 272, 274 to energizethe stack. It has been found that the rate of voltage rise across thestack should be controlled within certain limits to avoid arcing betweenthe positive and negative electrodes which are interleaved with thediscs in the stack. Such arcing, if not prevented, can lead to earlyfailure of the stack. The rise time of the 1000 volt pulse energizingsignal which is developed across the stack is limited by thecharacteristics of the inductors 272, 274. As the stack is energized, alarge expansive force is almost instantly developed to open the controlvalve 16 so that an injection of fuel to the cylinder can occur. Thetrailing edge of the pulse supplied from the power amplifier circuit 260is utilized to deenergize the piezoelectric stack. For this purposeanother transformer 278 is connected with the leads 262, 264. Adischarge circuit which includes an inductor 280 and another SCR 282 isconnected in circuit as shown. The coupling between the primary andsecondary of transformer 278 is opposite that of transformer 276 so thatthe trailing edge of the pulse from power amplifier 260 causes SCR 282to switch into conduction. When SCR 282 is in conduction, there is acharge on the piezoelectric stack because the stack electricallyexhibits a capacitance characteristic. The charge is drawn from thestack through the inductors 274 and 280 and through the SCR 282. Theinductor 280 serves to assist in energy storage rather than dissipatingenergy as heat. Additional storage capacitors 284, 286 are alsoconnected in circuit as shown and these serve to store a portion ofenergy which was utilized to actuate the piezoelectric stack. Thecapacitors 284 and 286 along with the diode 288 are connected in circuitas illustrated to provide for this additional energy storage. A voltagelimiter comprising a zener diode 290 and a resistor 292 are connectedacross the capacitor 286 to limit the maximum charge which can be heldby that capacitor, and thus limit the maximum reverse voltage across thestack to a safe level. The arrangement is such that once the circuit hasbeen energized and begins to cycle, only a portion of the energyrequired to actuate the stack is drawn from capacitor 268 during eachcycle, the remainder being supplied by the capacitor 284 since it willtend to aid the charging of the stack when it is desired to energize thevalve. The configuration of the inductors 272, 274, and 280 achievesoptimum performance for both charging and discharging the stack. Bothcapacitors 284 and 286 are shunted by respective resistors which may beswitched into the circuit during testing procedures to avoid shock tothe personnel who may be testing the circuit.

In operation of the system, pump and distributor assembly 12 is drivenby the engine to supply pressurized fuel via valve 22 and surge tank 24to inlet port 134 of control valve 16. The control circuit energizes thecontrol valve at the appropriate time to cause an amount of fuel to passthrough the control valve and via line 46 back to the distributorposition of assembly 12 which at that instant is establishingcommunication with the appropriate injector 14. Thus, a pilot pulse,followed by a main pulse, of fuel is injected into the appropriatecylinder. When valve 16 is de-energized, excess pressure in the circuitbetween the outlet 136 and the injector is relieved by fluid flow backthrough valve 16 to drain 162. Because the stack 70 experiences a highduty cycle, it tends to heat up rapidly. The cooling of the stack by thecirculation of liquid fuel through space 88 via lines 32 and 30 preventsshortening of the valve stroke which would otherwise occur uponoverheating of the stack and thereby avoids increased pressure dropbetween inlet 134 and outlet 136 which would occur with such shorteningof the stroke. While it is fully contemplated that the system of theinstant invention can be used to start the engine, it may beadvantageous to incorporate a separate conventional start system incertain instances which would be used only during the starting phase ofoperation until the engine is running fast enough to drive the pump anddistributor assembly 12 so that suitable line pressures can bedeveloped.

What is claimed is:
 1. In a fuel injection system a control valveadapted to control fuel flow to an injector mechanism comprising;a valvebody; an inlet, outlet and drain port in said body, said outlet beingconnected to said injector mechanism, said inlet being connected to asource of high pressure fuel and said drain port being connected to afuel reservoir; a first fluid passage within said body between saidinlet and said outlet; a second fluid passage within said bodyconnecting said outlet to said drain port; a valving element disposed insaid first passage to control flow therethrough, said valving elementhaving a first and second position, said valving element blocking fluidflow through said first passage in said first position and blockingfluid flow through said second passage in said second position; anelectro expansive actuator disposed in said valve body for said valvingelement to move said valving element from said first to said secondposition; an annular space in said valve body surrounding said actuator;and a second inlet connected to a source of low pressure fuel and asecond outlet connected to a return line to said fuel reservoir said lowpressure fuel flowing continuously into and out of said annular space tomaintain the electro-expansive actuator near ambient temperature andprevent the actuator's stroke from changing during operation.
 2. Acontrol valve in a fuel injection system as set forth in claim 1 whereinthe system includes a fuel tank, an inlet circuit including a pumpbetween the fuel tank and said additional inlet, and a return circuitbetween said additional outlet and the fuel tank.
 3. A control valve ina fuel injection system as set forth in claim 1 including a flow controlrestriction between said pump and said second inlet.
 4. A control valvein a fuel injection system as set forth in claim 1 wherein saidelectro-expansive actuator comprises a piezoelectric stack.